The process of reaction injection molding (RIM) has been rapidly developed and widely used in recent years. A variety of materials have been developed at the same time to utilize this process. Most of these materials, for instance polyurethane RIM and epoxy RIM, are thermoset polymers that are amorphous in nature. They generally have good mechanical strength and physical properties adequate for many automotive applications. For instance, polyurethane RIM has been widely used for automotive bumpers because of its good physical properties and its easy processibility.
In some applications such as automobile body panels, only materials having very high impact strength and thermal stability can be used. Since the body panels have to go through paint ovens, the heat distortion temperature of a polyurethane RIM cannot meet such requirement. To meet such high temperature requirement, other types of semi-crystalline RIM material of higher mechanical strength have recently been developed. One of such materials is a nylon-6 and polyurethane copolymer that can be processed by a RIM method. However, we have found that this material is not thermally stable and its physical properties are easily deteriorated by exposure to moisture.
It is therefore an object of the present invention to provide a nylon/polyurea copolymer processible by a RIM method which has good thermal stability.
It is yet another object of the present invention to provide a nylon/polyurea copolymer processible by a RIM method which has good thermal stability and impact strength adequate for use in high impact automotive applications.